Dielectric substrates are typically electroplated by first depositing a thin, electrically conductive film on the surface and then cathodizing the film in a desired metal electroplating bath (e.g., copper, nickel, chrome, etc.) to deposit the desired metal layer atop the conductive film. The thin conductive film may be applied by any of a number of techniques including chemical deposition, vapor deposition, sputtering, etc. For polymeric substrates such as acrylonitrile butadiene styrene (ABS) or phenylene oxide the most popular filming technique involves electroless chemical deposition of nickel or copper. A number of commercially available systems have been developed for this purpose including: the Crownplate.TM. system marketed by the Shipley Company; the Macuplex.TM. system marketed by the MacDermid Company; and the Enplate.TM. system marketed by Enthone, Inc. While each of these systems differs somewhat from the other they perform the same function in essentially the same way. In this regard, the surface is cleaned, etched (e.g., in chromic acid or chromic-sulfuric acid), catalyzed (i.e., with tin plus palladium salts or a tin/palladium colloid), immersed in a nickel or copper bath to chemically deposit a nickel/copper film on the surface, and finally electroplated as desired. A variety of rinsing and neutralizing steps are interspersed between the aforesaid essential steps.
Heretofore electroplating selective areas of dielectric substrates has typically involved masking off the substrate to define those areas where plating was sought and to cover, or otherwise render inactive, those other areas which, but for masking, would receive a significant amount of electrodeposit (i.e., otherwise in a high current density region of the substrate). Demasking of the substrate followed plating. Masking and demasking operations are performed either during the preplating steps (i.e., up through the electroless Ni or Cu filming steps) or more usually during the electroplating step itself. Masking and demasking operations are so cumbersome and time-consuming that many platers find it more practical to simply electroplate the entire surface rather than mask and demask a part for selective plating. Such efforts to avoid masking/demasking are highly inefficient in that they: consume excess electrolytic metal and electrolyzing current; and reduce the number of parts that can be plated at any one time.
It is the principal object of the present invention to provide a maskless process for efficiently electroplating selective regions of a dielectric substrate. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.